Activated carbon comes in a variety of forms. Initially, it was made in the form of granules or powder. More recently, it has been made in the form of a fabric known as charcoal cloth or carbon cloth. Activated carbon is used to adsorb undesirable components from the atmosphere or from a local environment. However, it is known that the effectiveness of activated carbon can be comprised by other components, not necessarily undesirable per se, that saturate the activated carbon and prevent it from adsorbing the undesirable components. The most common component that leads to such saturation of activated carbon is water.
Activated carbon is used in clothing to provide protection against undesirable components, but when such clothing is wet, the effectiveness of the activated carbon in adsorbing the undesirable component is drastically reduced. Also, the additional weight of such wet clothing presents a further disadvantage. To overcome this problem, carbon cloth is often used as one component in a composite structure that includes a relatively waterproof, outer fabric layer.
There is a problem associated with using such a waterproof barrier fabric as either the outer layer of a carbon cloth composite or the inner layer of such a composite. Because the barrier fabric cannot prevent moisture condensation on the activated carbon, liquids (e.g, sweat or water) can reach the activated carbon and inhibit its adsorption ability. Once the moisture has condensed on the surface of the activated carbon, the barrier fabric actually traps the moisture on the activated carbon, preventing evaporation. The so-called barrier fabrics are especially incapable of performing their intended role—that is, preserving the adsorptive properties of the activated carbon—in the laundering process, where the composite is exposed not only to large amounts of water, but also to detergents, soil, and other contaminants.
U.S. Pat. No. 4,732,805 to Maggs describes treating activated carbon with a fluorocarbon resin at add-on levels of 5% to 10% of the weight of the carbon cloth. The preferred fluorocarbon resin is polytetrafluoroethylene (PTFE) having a primary particle size of 0.1 microns. A major shortcoming with this approach, however, is that the PTFE particles, which are by their nature non-sticking, do not bond well under normal process temperatures, resulting in a treatment with very poor durability. PTFE typically requires temperatures of at least 300° C. for bonding. Indeed, it is unlikely that such treatment would withstand routine laundering procedures.
Accordingly, there is a clear need for a treatment for activated carbon that is durable with respect to multiple launderings and that is capable of maintaining practical levels of adsorption over time.